Background: Landslide hazard mapping is a fundamental tool for disaster management activities in fragile mountainous terrains. The main purpose of this study is to carry out landslide hazard assessment by weights-ofevidence modelling and prepare optimized mitigation map in the Higher Himalaya of Nepal. The modelling was performed within a geographical information system (GIS), to derive a landslide hazard map of the North-West marginal hills of the Achham. Thematic maps representing various factors that are related to landslide activity were generated using field data and GIS techniques. Landslide events of the old landslides were used to assess the Bayesian probability of landslides in each cell unit with respect to the causative factors. Results: The analysis suggests that geomorphological and human-related factors play significant roles in determining the probability value. The hazard map prepared with five hazard classes viz. Very high, High, Moderate, Low and Very Low was used to determine the location of prime causative factors responsible for instability. Spatial distribution of causative factor was correlated with the mechanism and scale of failure. For the mitigation of such shallow-seated failure, bioengineering techniques (i.e. grass plantation, shrubs plantation, tree plantation along with small scale civil engineering structures) are taken as cost-effective and sustainable measures for the least developed country like Nepal. Based on prime causitive factors and required bioengineering techniques for stabilization of unstable road side slopes, mitigation map is prepared having 14 classes of mitigation measures. Conclusion: The mitigation map reveled only 6.8% road side slopes require retaining structures however that more than half of the instable slope can be treated with simple vegetative techniques. Therefore, high hazard doensnot demand expensive structures to mitigate it in each every case.

No abstract

Numerous engineering and environmental issues can be resolved using the bacterial-induced calcite precipitation (BCP), which has the potential to be environmentally friendly, sustainable, and economical. In BCP, bacterial enzymes used substrates and divalent cations to bind negatively charged ions to the bacterial surface and produce biocementation. Various metabolic pathways involved in the calcite precipitation and ureolysis are the principal bacterial pathways that have been illustrated by most bacteria including Sporosarcina pasteurii, Bacillus subtilis, and Pseudomonas putida. Ammonia is produced by these bacteria, which is toxic and should be eliminated. Therefore, BCP via carbonic anhydrase could be a preferred option because the end-products are not toxic. The growing global requirement of ground improvement boosted the demand for biostabilization because of its numerous benefits, including environmental issues. Dust suppression, remediated soil contaminants, polychlorinated biphenyl calcium ions, and CO2 sequestration, proving that BCP is environmentally friendly and sustainable. Furthermore, for fine-grained soils having pores smaller than 0.5 μm, the enzyme-induced calcite that uses enzymes instead of bacteria is more suitable to stabilize the soil by precipitating the calcite. The use of BCP as binders for soil stability and strengthening, innovative construction materials, subsurface barriers, and impermeable crusts is an emerging field. Calcite precipitated in the pores increases strength more than 20 times, resulting in a significant reduction in compressibility. Similarly, reduced soil permeability to up to 99% broadens its applicability. This review argues that BCP can be induced by multiple approaches, including urease expressing bacteria and carbonic anhydrase expressing bacteria as well as free enzymes.

No abstract